The present disclosure generally relates to systems and methods for producing laser beams at stabilized frequencies and powers.
An optical WDM system uses a single fiber link to simultaneously transmit optical carriers of different wavelengths so that different channels of data can be carried by the different carriers and sent over the optical fiber link at the same time. The optical signal in such a fiber link is a WDM signal because it is a combination of different optical carriers at different wavelengths. Hence, a WDM system can provide a broadband transmission and a high transmission speed. Dense WDM (DWDM) techniques have been used to increase the number of multiplexed wavelengths in a WDM fiber link by reducing the wavelength spacing between two adjacent wavelengths. In addition, a WDM system can be made scalable to allow expansion of the transmission capacity by simply adding the number of optical carriers in the existing fiber links without adding new fiber links.
To increase the bandwidth and the number of communication channels in WDM networks, the International Telecommunications Union (ITU) has proposed the DWDM system in which the separation between communication channels is only 0.8 nm, or 100 GHz in frequency. Thus, a light source for such a network must also have a very narrow output linewidth. This requirement entails having the wavelength of the output signal to be concentrated in a very narrow portion of the optical spectrum. Further, the wavelength of the source must be stable to avoid drifting into the wavelength range of another channel.
Conventional wavelength lockers monitor and control the wavelength of light produced by a light source such as a laser. A laser is typically tuned to produce light of a predetermined wavelength. However, a number of internal and external factors may cause the laser wavelength to change or drift. For example, in a diode case, the driving current can change the resonant characteristics of the cavity. Consequently, the wavelength of the light produced by a laser drifts from the predetermined wavelength. Other factors, such as shot noise, temperature fluctuation, and mechanical vibrations, may also change the laser wavelength.
Wavelength locking mechanisms have been used to stabilize a laser at a desired wavelength. In some wavelength locking mechanisms, for example, light from the laser is transmitted to a collimator, and travels down a fiber. Conventional systems monitor the wavelength of the incoming light by transmitting the beam to a spectrum analyzer. The spectrum analyzer determines the wavelengths that comprise the beam of light. The spectrum analyzer transfers the information on the wavelength to a feedback system. The feedback system uses this information to change the temperature or other laser parameters to compensate for any drift in the wavelength of the light from the predetermined value. The temperature is often controlled using a thermo-electric (TE) pad or cooler.
In recognition of the above-described difficulties, the inventors recognized the need for providing a laser system in which the wavelength and power of the transmitted light is monitored and controlled without significant interruption of the light. Further, a need exists for a system that is cheaper and easier to manufacture.
The present disclosure describes a laser array system. The system includes a plurality of lasers, a switching mechanism, a wavelength locking mechanism, and a laser parameter feedback control.
Each laser provides a collimated beam having certain wavelength and power. The beam has at least two parts, first part of the two parts used for stabilization of the wavelength and power. The switching mechanism is configured to receive and sequentially select the first part of the collimated beam from the plurality of lasers. The wavelength locking mechanism is configured to monitor and measure a drift of the wavelength and power of a selected laser. The laser parameter feedback control is configured to adjust laser parameters of the selected laser.